The present invention relates to a charged particle beam irradiation apparatus for use in the writing and measurement of a micropattern on a semiconductor device and, in particular, a charged particle beam irradiation apparatus having an improved reflection prevention board over a sample surface.
In the lithography process of the-state-of-the-art semiconductor manufacturing process, it is expected that an electronic beam writing type will become a future main-stream technique. The reason is that the electron beam writing method is outstandingly higher in image resolution than the light beam writing method.
The electronic beam writing apparatus is used for forming an etching mask on a sample for example. As shown in FIG. 1, an electron beam narrowly stopped down by an objective lens 61 is directed onto a resist 62 coated on a sample 63, such as a mask, a wafer, etc., and the resist 62 is scanned with the electron beam. A pattern is formed on the resist 62. And an etching mask is completed by doing so.
A portion of the electron beam thus directed for irradiation is reflected on the surface of the sample 63. Secondary electrons are produced from the sample 63. Some of the reflected electrons and secondary electrons 73 are reflected on the lower surface of the objective lens 61 and back onto the resist 62, resulting in an error occurring on the resist 62. Those reflected and secondary electrons 74 returned back onto the resist 62 are light-sensitized at other than a target location, resulting in a lowering in writing precision. In order to reduce such an error, a reflection prevention board is attached to the lower surface of the objective lens 61, the sheet being made of a material of a lower atomic number, such as a carbon.
As a demand for a write precision becomes higher and higher, no adequate reflection preventing effect is obtained from the reflection prevention board made of the lower atomic number material. In order to improve the reflection prevention effect, proposals are made to provide a reflection prevention board with microholes opened perpendicular to the sheet. Further, as shown in FIG. 2, a proposal is also made to provide a honeycomb type reflection prevention board with a dense array of hexagonally prismatic microholes.
However, the proposed reflection prevention board has the following problems (1) and (2):
(1) The deeper the microholes in the reflection prevention board, that is, the thicker the reflection prevention board, the higher the reflection prevention effect. In general, with the microhole diameter set to 0.8 mm, at least 4 mm-thick sheet is preferable as the reflection prevention board. It is difficult, however, to form a regular honeycomb array of microholes in such a thick metal sheet by the mechanical working technique. And more working time is taken and, in spite of this, a poor yield and a very high manufacturing cost result. A proposal is also made to use the technique for metal-plating those holes in a thick-film resist patterned by an LIGA process, that is, the X-ray lithography. The LIGA process involves the problem of the reflection prevention board involving an upper size limitation and very high manufacturing cost.
(2) The conventional reflection prevention board can effectively prevent those vertically incident reflection electrons and secondary electrons. As shown, for example, in FIG. 3, it is not possible to effectively prevent those obliquely incident reflection electrons and secondary electrons. The reason is that the obliquely incident reflection electrons are reflected on the sidewall of the microhole and bounced out of the microhole.
As seen from the above, the existing reflection prevention board used in the electron beam writing apparatus presents the problems of being high in manufacturing cost, being unable to provide deeper microholes and being unable to effectively preventing the obliquely incident reflection electrons and secondary electrons.